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Thread: Painting Metal

  1. #1

    Painting Metal

    Hi guys. I'm pretty new here so I find myself asking a lot of questions about things that have crossed my mind from time to time.

    Painted metal. Examples: my coffee table has metal of some kind wrapped around each leg, and then welded to cross members. My patio set has shaped and welded metal on the chairs and table frames. These are all black.

    How is this stuff painted with such a durable finish? I would like to make (after I learn to weld - lol) a table with rectangular metal legs. I know for a fact if I hit that framing with Krylon it would scrape off with a fingernail, even with a sanded scuff finish on the metal and a primer coat.

    Inquiring minds want to know.

    Thanks.

  2. #2
    Join Date
    Feb 2007
    Location
    southeast Michigan
    Posts
    676
    Michael, you are correct about a durable paint finish on metal. I have sprayed some smaller parts with regular spray paint like Rustoleum and baked them in an oven which adds to the durability. Most metal things you buy nowadays is powder coated. This is a process in which the metal part is electrostatically charged so the powder will stick only to it and then the part is cured under heat. This produces a very durable finish and is a cost saver for manufacturers since there is no wasted overspray.

    If you plan to do a lot of smaller parts it might be worth the investment to do at home. But for a larger project you should be able to find a local source that can do it for you. Others can chime in if there's a 2 part epoxy paint that can be used but I know that any epoxy rattle can paint you buy isn't worth a hoot.

  3. #3
    Join Date
    Apr 2016
    Location
    Tasmania
    Posts
    2,162
    Michael, John has correctly pointed out that many mass produced consumer items are powder coated. It's a process that suits industrial processing and gets a marketable appearance. Make your table frame or whatever and take it to a contract powder coat workshop and it won't cost much.

    Protecting steel from corrosion is a whole industry in itself. What coating or process is best depends on the environment. In your own house you can observe that things rust at different rates in the bathroom, sitting room or on the patio. Same steel, different environment. There are a countless types of coatings out there but you can get a reasonable result for household/workshop items with commonly available products.

    Here are some rules.

    Design the job so you don't end up with areas that you can't paint. Make sure there are no pockets that can hold water. Anywhere paint can't cover will rust.

    Prepare the surface of the steel. This includes grinding all edges to a small radius as paint won't cling to sharp edges. Remove any weld spatter - paint won't cling around it either. Check all welds are neat and without porosity. At this stage you should be able to run your bare hands all over the job with no risk of blood loss. Clean everything

    The next stage of surface preparation is to abrade the steel to provide a clean surface for paint application. If it is old steel, remove all the old paint and rust. The best way is to get it sand blasted but if it is small, grinding/sanding etc will work. It's actually better to clean the components individually before welding if using recycled steel. Welding hates dirty steel. Whichever way, you need a surface that is clean and at least 70% bright steel with no loose rust.

    If you think that is a lot of work, you are correct. That is 2/3 of the whole job and you haven't even gotten out a paint tin yet.

    You need to get the primer on as soon as possible. If you have to leave it overnight unpainted, give it a quick rub over with sandpaper and blow it down again.

    Use a primer that contains zinc phosphate. You can also use a straight zinc primer but it will be more expensive. Both are rust inhibitive primers. Choose your own brand but don't waste your money at a big box home hardware shop. Go to either an auto accessories or an auto paint store. You will get spray cans or larger cans of paint that is going to work. Get the primer and get the top coat at the same time and use the same brand. There is no risk of incompatibility then. Get the shop to print a copy of the tech data sheets for the paints and follow the instructions for application technique, thickness and cure times.

    That gets a basic job done. The standard improves with different classes of coating. You can go to powder coat, acrylic, epoxy, polyurethane, polyaspartic, polysiloxane, etc etc all of which have sub classes and variants that perform better in specific environments. The work I do requires solutions to protect steel in different environments so our store has about a dozen different coating types on the shelf that get specified on a project by project basis. Hope this gives you some insight. Cheers

  4. #4
    Wow... and thanks. Where are you located Wayne?

  5. #5
    Join Date
    Feb 2003
    Location
    McKinney, TX
    Posts
    2,060
    Look to the right from Wayne’s name and you will see his location
    Steve Jenkins, McKinney, TX. 469 742-9694
    Always use the word "impossible" with extreme caution

  6. #6
    Join Date
    Apr 2016
    Location
    Tasmania
    Posts
    2,162
    Yes, as Steve said, Tasmania. The main part of my life these days is managing a CNC machining and abrasive blasting/industrial painting shop where we paint heavy marine mooring equipment for global export (just about to dispatch another order to the USA). I used to contract all over Australia doing joinery, furniture, construction and heavy industrial painting (bridges, oil refineries, power stations etc). Cheers
    Every construction obeys the laws of physics. Whether we like or understand the result is of no interest to the universe.

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